Detalles de publicación

PP 020106

The Milky Way's bulge star formation history as constrained from its bimodal chemical abundance distribution

J. Lian, G. Zasowski, S. Hasselquist, D. M. Nataf, D. Thomas, C. M. Bidin, J. G. Fernández-Trincado, D. A. Garcia-Hernandez, R. R. Lane, S. R. Majewski, A. Roman-Lopes, M. Schultheis
Several institutions from North and South America and Europe (including IAC and ULL)
We conduct a quantitative analysis of the star formation history (SFH) of the Milky Way's bulge by exploiting the constraining power of its stellar [Fe/H] and [Mg/Fe] distribution functions. Using APOGEE data, we confirm the previously-established bimodal [Mg/Fe]-[Fe/H] distribution within 3 kpc of the inner Galaxy. Compared to that in the solar vicinity, the high-alpha population in the bulge peaks at a lower [Fe/H]. To fit these observations, we use a simple but flexible star formation framework, which assumes two distinct stages of gas accretion and star formation, and systematically evaluate a wide multi-dimensional parameter space. We find that the data favor a three-phase SFH that consists of an initial starburst, followed by a rapid star formation quenching episode and a lengthy, quiescent secular evolution phase. The metal-poor, high-alpha bulge stars ([Fe/H]<0.0 and [Mg/Fe]>0.15) are formed rapidly (<2 Gyr) during the early starburst. The density gap between the high- and low-alpha sequences is due to the quenching process. The metal-rich, low-alpha population ([Fe/H]>0.0 and [Mg/Fe]<0.15) then accumulates gradually through inefficient star formation during the secular phase. This is qualitatively consistent with the early SFH of the inner disk. Given this scenario, a notable fraction of young stars (age<5 Gyr) is expected to persist in the bulge. Combined with extragalactic observations, these results suggest that a rapid star formation quenching process is responsible for bimodal distributions in both the Milky Way's stellar populations and in the general galaxy population and thus plays a critical role in galaxy evolution.

 
Aceptado para publicación en MNRAS | Enviado el 2020-07-27 | Proyecto P/308615